Dubois by country mile. Wilder has no legs. The moment Dubois start landing will be the moment Wilder start crawling on the canvas. Wilder never ever in his life beat a prime fighter. Hell he never fought one. Also the Wilder - Miller sparring rumours are irrelevant. Just a rumour. Like the Fury - Opetaia one and every other rumours out there. Sparing is completely different than the actual fight. Also i don't buy it, and the reason is Miller is American and he was unbeaten, and somehow of a known name in the HW division. If that was the case Wilder would 100% wanted to fight him and take that W on his lacking resume. Miller would easily be top 2 best win for Wilder.
Hard to know or care. Both men are/were massively manufactured products. Wilder is the more naturally springy and unorthodox guy with the ability to turn the tables at any time, while Dubois is the more orthodox and well-schooled fighter with decent power but tends to be extremely stiff and unimaginative. Either Wilder gets befuddled by Dubois's rudimentary skills and takes a beating or he gets befuddled by Dubois's rudimentary skills, takes a beating, but manages to land a fight-ender and Dubois quits. This is basically the fight that lots of people thought Wilder vs Joshua would be till they realised the actual gulf in class between the two fighters.
I don't think we will ever see that Wilder again. Joshua vs Wilder should have happened right before or right after Wilder's 1st round KO of Dominic Breazele. Of course Eddie Hearn likely knew Joshua would have been savagely KO'd by that Wilder hence why he hesitated making that fight for so long.